Tuning mechanism for resonant cavities and the like



March 28, 1950 G. MARTI'N 2,501,728

TUNING MECHANISM FOR RESONANT CAVITIES .AND THE LIKE Filed May 25, 1944 I EDWARD G. MARTIN Patented Mar. 28, 1950 TUNING MECHANISM FOR RESONANT CAVITIES AND THE LIKE Edward G. Martin, Cambridge, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application May 25, 1944, Serial No. 537,280

2 Claims.

This invention relates to a mechanism for tuning magnetron oscillators, cavity resonators and the like.

It is an object of this invention to provide a simple, compact and rugged mechanism for imparting lateral motion to a flexible diaphragm which is disposed in the head of a magnetron os cillator or other resonant cavity, in such a manner as to effect a tuning of the same thereby.

Other objects and features of the present invention will become apparent upon a careful consideration of the following detailed description when taken together with the accompanying drawings in which:

Figure 1 is a cross-sectional view, taken through the center of a tuning mechanism constructed in accordance with the teachings of this invention and showing in part a magnetron oscillator and its relation to the tuning mechanism; and Fig. 2 is a cross-sectional view taken through the center of the tuning mechanism parallel to the axis and showing one possible modification of the invention.

In the arrangement shown in Fig. 1 the tuning mechanism is adapted to tune a magnetron oscillator of the type which is typical to that now known to the art. The magnetron consists of a cylindrical anode block l into which several cylindrical resonators shown at II and II' are bored usually at equal angular points about the center of the anode. Each of the resonators opens into a slot, one face of which is shown at l2 and I2 which in turn opens radially into the center bore I3 of the anode. The resonators and respective slots are so dimensioned as to resonate at the desired frequency of operation, which is stabilized by a pair of strapping rings disposed on opposite faces of the anode and connected to alternate anode segments. One strapping ring I4 is shown at the top face of the anode. Concentrically disposed within the central bore l3 of the anode I0 is an indirectly heated cathode IS, the filamentary leads and supports for which are here omitted in order to simplify the illustration, as is the magnet which accompanies the usual magnetron.

Also as shown, the tuning mechanism comprises a threaded nut member 3 which is securely fixed to a circular flange gear 8 which in turn engages the teeth of a drive gear H5. The nut 3 is supported in the head of the magnetron by a spring loaded ball bearing arrangement consisting of the balls 5, two circular beveled members 4 and 6 which constitute the outer race and a circular Phosphor bronze spring 'I which in turn is secured to a support member I! by means of the machine screws l8. Also provided but not shown is a knurled nut or other suitable hand operated means attached to the shaft IQ of the drive gear 16. Thus as the nut 3 is rotated by the drive gear 16 and flange gear 8 a lead screw I which engages the threads of nut 3 is caused to move laterally. Securely fixed to the lead screw l and adapted to flex therewith is a thin flexible diaphragm 2 which is also secured at its outer edges to the support l1. Thus as lead screw l is moved laterally, diaphragm 2 is flexed correspondingly thereby tuning the magnetron. The tuning is believed to result from the fact that the diaphragm 2 produces a capacitance in shunt with the capacitance between the adjacent faces [2 of the slots. A discrete advantage afforded by this mechanism is that it minimizes both the driving torque required at gear I6 and back lash of nut 3. That is, the balls 5 are always held in snug relation to the races by means of the force exerted on the upper section 6 of the outer race by the spring 1, thus minimizing the lateral play of nut 3.

Another advantage of this invention is the comparative ease of manufacture and assembly of the tuning mechanism over those of the prior art. The lower stationary race 4 and nut 3 are first inserted in the head of the magnetron or other resonant cavity. The balls 5 and upper race 6 are then inserted and held in position by the Phosphor bronze spring I, after which the flange gear 8 is fastened to the nut 3 by the machine screws 9. It has also been found that this mechanism is less sensitive to temperature and pressure changes than those offered by the prior art.

A second arrangement which may also be used to an advantage is illustrated in Fig. 2. In this arrangement the lead screw I which is used to flex the diaphragm 2 again engages the rotatable nut 3 which in this case contains a circular flange 20 at one end thereof, beveled at its outer edge so as to project in between two sets of balls 5 and 5' which are held by the upper and lower sections 6 and 4 of the outer race and the circular metallic spring number 1.

Although I have shown and described only certain and specific embodiments of the present invention I am fully aware of the many modifications possible thereof. Therefore this invention is not to be limited except insofar as is necessitated by the prior art and the spirit of the appended claims.

I claim:

1. A tuning mechanism for cavity resonators and the like, comprising a flexible diaphragm disposed in one end of said cavity and secured at its outer edges thereto, a nut supported at the same said one end by means of a ball bearing, said ball bearing comprising an inner race out in said nut and an outer race formed by an upper and lower section, a circular Phosphor bronze spring adapted to exert a force on said upper section of said outer race and thereby hold the balls of said ball bearing in snug relation to both said races, a lead screw secured to said diaphragm at a central point thereof, and adapted.

to engage the threads of said nut, a circular flange gear secured to said nut and a manually adjusted drive gear arranged to mesh with said flange gear so as to impart lateral motion to said lead screw thereby flexing said diaphragm correspondingly whenever said drive gear is operated.

2. A tuning mechanism for a cavity resonator comprising, a flexible diaphragm disposed at an end of said resonator, a nut, a supporting structure including a ball bearing being secured to said resonator, said ball bearing maintaining 4 said nut in spaced relationship with said diaphragm, said bearing comprising an inner race cut in said nut and an outer race formed of separated sections, resilient means biasing said sections together, a lead screw secured to said diaphragm at a central point thereof and adapted to engage the threads of said nut, a circular gear secured to said nut, and a drive gear in meshed relationship with said circular ear.

EDWARD G. MARTIN.

REFERENCES CITED The following references are of record in the file 02- this patent:

UNITED STATES PATENTS Number Name Date 1,606,127 Kolb Nov. 9, 1926 1,886,219 Parker Nov. 1, 1932 2,117,090 Grundmann May 10, 1938 2,242,275 Varian May 20, 1941 2,259,690 Hansen et a1 Oct. 21, 1941 2,409,321 Stephan Oct. 15, 1946 2,439,388 Hansen Apr. 13, 1948 

